Vacuum or thermionic tube



July 19, 1927.

A. G. THOMAS VACUUM 0R THERMIONIC' TUBE Filed Ana. 2, 1923 Patented-July19; 1927.

UNITED STATES,

PATENT-OFFICE;-

ALBEBJ. G. THOMAS, OI L YNCHBU BG, VIRGINIA.

vacuum on 'rnsmnomc runs. j

Application filed August a, 1928. Serial no. 855,818.

This invention relates to new and useful constructions and dispositionsof'the ele-' ments of vacuum or thermlomc tubes such centration of thegrid-filament field and of the electronic stream at or near the point ofaction of the grid. Another object is to attain this reduction andconcentration by mechanical construction of the elements and bydisposition of suitable sources of electrical energy. Further objectsare to provide cathodes of larger emissive area, and to dispose the gridout of the direct trajectory of the electrons assing to the plate, soit'no I lon er is an obstacle to the passage of some of t 1e electrons.

WVith these and other objects in view, as will appear in the followingspecifications, I have represented some exemplifications of theconstruction of such tubes in the accompanying drawings, in which:

Fig. 1 is a diagrammatic presentation of a tube with a related circuit;

Fig. 2 is a similar view of a modified tube, with a related circuit;

Fig. 3 is a further modification, with a related circuit;

Fig. 4 shows a modification of the tube of Fig. 1.

In all of these figures,-F represents thefilament of tungsten, thoriatedplatinum, or

her, and P isthe plate or receiving member. 1 indicates the evacuatedglass tube or vessel for containing the several elements. A is thebattery for heating the filament F, and R is the correspondingregulating rheostat. The antenna circuit in each case com rises theantenna v8, the series condenser induc-- tance L, and the ground 11. Thesecondary circuit comprises the inductance L? in variableelectromagnetic relation with L, and a tuning condenser C; a grid leak14'and grid condenser 15 have the customary place and functions. a Thetelephone or-other a is designated'by T, and the battery or fur-- catorof received and detected si nishing the filament-plate current andrendering the plate positive with regard to the filament at B. Thevarious elements are shown. diagrammatically, and in practice the like.G is the grid or controlling memsequent strong'fiel may be supported andi etained withinthe vessel 1 in any appropriate manner. f In Fig. 1, isshown a tube havinga filament F which may be in a straight line asshown,' or wound spirally to conform to the shape of the element Fdisposed about it since its object is to heat .the element F"byradiation and bombardment, the particular shape is unimportant.Surrounding and coaxial with the filament F is a cylindrical orVenturi-tube shaped element F. of uniform thickness, which forms theemissive cathode proper. It is shown as shaped asa figure of revolution,i. e., like a Venturi tube or a" pulley, with an external groove havinga circular section, with the center of this'circle at the intersticebetween .the grid rin G. It is preferablycoated on the outsi e, 01' theside nextthe grid elements, with sodium, thorium or othereasilyionizable inaterial. The grids G are two dished rings coaxial.with the filament F and element F, and disposed at a distance apartslightly greater than the thickn s of the electronic stream. The plateis formed as a cylinder P coaxial with the filament F, and may beVenturi-shaped to correspond. to element F. The circuit connections areas usual, with the addition of the battery B, between filament andcathode F, to make the filament negative with regard to the cathode. Theheating of the cathode F determines an emission of electrons, which tendto depart in a direction normal to "the surface, and thus to passthrough the interstice between the grid rings G. The small area and sizeof the grid members entails a high concen-*. tration of the change uponthem with a conand thus agreat amplification of the signal. It should beespecially noted thatflthe grids G are entirely out of the trajectory ofthe electronic stream, and therefore do not form a physical obstacle-tothe passa of the stream.

In' Fig. 2, the ament F is. reb'ent and a curved to occupy a sphericalsurface concentric to F, to enable the filament F to have the greatesteffect upon F. The cathode F" is-hereiormed'asacurvedreflectonpreferably spherical, focus'sed r centered upon a spot 0;a battery B or other source :keep's F negative with respect to F andthe electronic stream leaves the reflector normal to its surface andtherefore p through a cal surface similar to Y centered about 0;preferabl it pro ects very its geometrical center, or nearly so, is asmall cylindrical grid G. The late -P is a spheriand likewise is littlebeyond the area struc by the cone of electrons passing through the grid.As before, the materlal of which G is composed may be any, as strips,mesh, etc.

The operation of Fig. 2 is similar to that of Fi 1. The principaldifference in the two figures is that here the electrons are focussed ata point; while in Fig. 1 they are focussed at a circular line betweenthe grids. The dotted lines indicate paths of electrons passing fromcathode to plate.

, Fig. 3 has the filament F disposed next the grid which is formed as ahollow surface G such as a cylinder or toroid on either side of thefocus of the filament F, which is rebent and curved to' c lindricalshape. Behind the filamentlF is isposed a cylindrical reflector S ofmetal,.which is charged to a high ne ative potential with regard to thefilament y a battery B. In the draw.- ings, the reflector S and filamentF have been conventionally shown as having cross sections inthe form ofcircular arcs: but it will be understood that the len h of the cylindersin each instance may be etermined by the designer according to the knownrules of active surface requirements, etc.

ria

This reflector causes the electrons. emitted from the filament to movein directions normal to thecylindersF and S and radial tov the focus 0,and prevents the emission of electrons in a direction opposite to thatfrom filament to grid. The plate P is either plane of. cylindrical about0 as a center and is constructed of such size as not to extendappreciably' beyond the area enclosed by the lines of the grid. Hereagain the grld-filament electrostatic field is very much concentrated atO, and a great proportional change in the late-filament current occurs.The filament s preferably made of ribbon shaped mate- Fig. 4 shows asimilar to that in Fig.

' 1, but has the filament itself curled into a spiral of the shapeindicated for the cathode F of Fig. 1. It therefore itself both emitsthe electrons and directs themnormal toits general-bounding surface. Thegrids G, G are formed as two parallel rin s separated by an intersticeof such width t at thereonverging eI QtI'OIIS are afforded unobstructedL "passage from the filament F to the plateP,

which in thiscase has plane or curved-surface.

The circuits shown are appropriate for use withthese tubes, although anypresent ode, said axis being on t e convex side of lution generated :bythe movement of an are about an axis of symmetr within the oathsaid areand in its plane whereby. electrons emitted in paths normal to saidsurface converge upon a circle having its center at said axis.

2. Inan electron discharge tube, a'filament, a hollow cathode ofcircular cross section concentric with said filament, said cathodehaving its outer surface of arcuate section in a plane passing throughthe filament, said surface being directed away from said filament, acircular grid structure concentric with said filament and cathode andlocated adjacent the center of curvature of said cathode section, and ananode.

3. In an electron dischar e tube, a cathode 55 having the external form0 a fi e of revolution generated by the revolutionlof a circular arcabout a line in the plane of the arc and on the side thereof oppositeits center, two grid rin s of the diameter of and located adjacent anparallel to and coaxial with .the imaginary circle traversed by thecenter trons emitted in a focused stream from said cathode, and ananode. Y

4. In an electron discharge tube, a cathode adapted to emit electrons,said cathode having its external surface formed as a figure ofrevolution generated by an arcuate line moving about an axis on theconvex side of the arcuate line, so that the emitted electrons arefocused upon a circle, rid rings disposed'parallel to the said circ e,and an anode. 5. In an electron discharge tube, a cathode having asurface adapted to emit electrons, said surface being a figure ofrevolution generated by the movement of an arc about an axis lying inits own plane and onthe con- 119 vex sidew-qff the arc whereby electronsemitted in paths normal to the said surface conver e said circle, and ananode.

--6.' In an electron dischargetube,a cathode having the external form 0a figure of revolution generated by the revolution of an arc about aline in the plane of and on the convex side of the arc.

In testimony whereofI afiix my signature.

ALBERT G. THOMAS.

